The present invention provides a magnetic recording medium and a magnetic recording reproducer which are excellent in sliding durability, and it can be widely utilized as a technique for lubricating sliding portions in general industrial machines.
Magnetic media are most generally used as information regenerators and are widespread in the fields of not only large computers but also small personal computers, word processors and the like. Therefore, the storage capacity of the magnetic media is increased year by year, and with this increase, a remarkable technical innovation has been made. Particularly in hard-type magnetic disc units requiring high packing density and high-speed writing, among magnetic recorders, thin film magnetic recording media capable of having a high packing density have been used in recent years. In the magnetic discs, the distance between a head and a disc tends to be reduced for increasing the storage capacity, and now the distance from the head is as short as about 0.1 .mu.m. Therefore, the probability of contact sliding of the head and the disc on each other is high not only during suspension of operation but also during operation of the disc. For this reason and the like, sliding conditions becomes severe unavoidably and hence sliding durability of the disc is absolutely necessary for improving the reliability of the magnetic disc units.
Now, the lubricating layers of most magnetic recording media are formed of fluoro compounds, and large number of attempts have been made to improve the sliding durability. For example, methods comprising coating with or chemical fixing of fluorine-containing lubricants capable of being easily adsorbed have been proposed in U.S. Pat. No. 4,120,995, Japanese Patent Unexamined Publication Nos. 54-36171, 59-172159, 59-203239, 60-38730, 60-109028, 60-101717, 60-101715, 60-242518, 60-202533, 60-246020, 61-39919, 61-104318, 62-42316, 63-225918 and 63-220420, etc. The fluorine-containing lubricants described in these references are silane-based and phosphoric acid-based lubricants which react with the surface of an inorganic thin protective layer on the magnetic layer of a thin film magnetic recording medium to adhere to the surface. In addition, methods for improving the sliding durability by forming a lubricating film consisting of a plurality of components on the surface of a disc have been proposed in Japanese Patent Unexamined Publication Nos. 62-257622, 62-257623, 2-175791, 2-240828, 2-249130, 3-34121 and 4-48435. Furthermore, methods comprising forming a lubricating film on a magnetic head slider in a contact portion with the surface of a disc have been proposed in Japanese Patent Unexamined Publication Nos. 62-188012, 62-231411, 62-34392, 63-48674, 63-117379, 63-269384, 63-276769, 1-137484 and 3-88189, etc. These techniques are suitable for the keeping-off of a head by the use of an air film, which is employed in present-day magnetic recorders.
However, the distance from a head tends to be reduced more and more in future, and it is considered that in the near future, the distance from a head will be of the order of nanometer or will become such that complete contact occurs. In such a range corresponding to keeping-off at a very short distance or contact sliding, a sufficient reliability on resistance to sliding cannot be realized by the above-mentioned conventional lubricating methods. Therefore, a lubricating layer formed on the outermost surface of a magnetic recording medium is required to have performance characteristics sufficient to withstand severe sliding conditions. In addition, magnetic recording media to be subjected to contact sliding, such as magnetic tapes should also be improved in sliding durability.
In these circumstances, methods in which a head is kept off using a thin liquid film have been proposed as techniques for lubrication in a range corresponding to keeping-off at a very short distance or at a completely contacted state, in U.S. Pat. Nos. 2,969,435 and 3,579,212, and Japanese Patent Unexamined Publication Nos. 63-308775, 2-249177, 2-130789 and 3-119580. The above invention in which a head is kept off by inserting a liquid film permits relatively stable keeping-off of the head even in the range corresponding to keeping-off at a very short distance, because the liquid film has a higher rigidity than does an air film. However, even when these techniques are employed for maintaining the reliability on sliding, contact sliding of a disc and the head on each other promotes the wear of the disc unless the liquid film for keeping-off the head has a high sliding durability in itself. Therefore, for coping with the above-mentioned severe sliding, it is necessary to impart functions such as high wear resistance and low frictional properties to the liquid film. But, there is no effective means for the impartment.
When recording and reading out are carried out while a head is kept off at a very short distance or is in complete contact with a disc, the head and the disc are brought into a severe sliding state because the contact sliding time is increased as compared with conventional sliding. Under such severe sliding conditions, the peeling-off of a lubricating film results in an accelerated increase of the wear of the disc. Even when the lubricating film is tightly fixed to the surface of a protective film by chemical bonding or the like, the peeling-off by sliding is not avoidable, so that the wear occurs intermittently. That is, even when the conventional method comprising forming a thin lubricating film of a fluoro compound on the surface of a disc which has been proposed in the above U.S. Pat. No. 4,120,995 and the like, is applied to keeping-off at a very short distance or complete contact sliding, the peeling-off by sliding of the lubricating film is not avoidable, so that the wear proceeds intermittently.
For preventing the wear of a disc during keeping-off at a very short distance or complete contact sliding, friction and wear should be kept slight by preventing always solid-solid contact between the sliding surface of a magnetic head slider and the surfaces of a protective film and a magnetic film. That is, recording and reading out can be maintained while keeping the friction between a head and the disc slight without their wear, when a lubricant having low frictional properties and an excellent wear resistance is used in the form of a lubricating film and the lubricating film is such that when a part of the lubricating film is peeled off by sliding, the lubricating film is repaired at once in the sliding portion.
The keeping-off methods using a thin liquid film which have been proposed in U.S. Pat. Nos. 2,969,435 and 3,579,212 and Japanese Patent Unexamined Publication Nos. 63-308775, 2-249177, 2-130789 and 3-119580 are considered effective as methods for repairing the peeled portion of a lubricating layer (a liquid film) because the liquid film always coats the sliding surface by continuous supply of liquid. However, when sliding is caused by contact between solids, the repair of the lubricating layer (the liquid film) by the supply of the liquid cannot prevent the occurrence and progress of wear unless the liquid used has a low viscosity for realizing keeping-off at a very short distance and the liquid supplied itself has satisfactory lubricating characteristics.
That is, as a lubricating method for keeping-off at a very short distance or complete contact sliding, the keeping-off methods using a liquid film, not to mention conventional methods comprising forming a thin lubricating film of a fluoro compound, are not sufficient. A problem to be solved by the present invention is to achieve impartment of ability to repair a lubricating film and a high sliding durability of the lubricating film itself, which is a problem in keeping-off at a very short distance or complete contact sliding. In detail, the problem to be solved by the present invention is to provide a magnetic recording medium and a magnetic recording reproducer which have been freed of problems in prior arts by a means for continuous supply of a liquid having a low viscosity, an excellent wear resistance and low frictional characteristics to sliding portions.